Eight Massachusetts Bay Transportation Authority vehicles derailed in 2016, the nation’s highest overall figure and the second consecutive year the transit agency has had among the most light-rail derailments in the country, according to federal statistics.

Last year, six Green Line trolleys and two subway maintenance vehicles derailed, according to data from the National Transit Database, which tracks safety data for transportation systems.

The New Orleans Regional Transit Authority and the San Francisco Municipal Railway each had six derailments across their systems, while the Washington Metropolitan Area Transit Authority and the Greater Cleveland Regional Transit Authority each had five.

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Safety experts said derailments are worrisome and must be addressed. And while nobody was hurt, delays often result.

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“A derailment is very rare,” said Monica Meade, a planner at WSP/Parsons Brinckerhoff, a worldwide engineering and design firm. Meade also helps lead the light rail committee of the nonprofit Transportation Research Board.

“If it’s an issue and if they find cars are derailing, they need to figure out why,” Meade said.

Officials have said the MBTA’s system is safe and the number of derailments is relatively low, given the number of trains on the Green Line, the busiest light rail line in the country.

No passengers or employees were hurt during any of the 2016 incidents, and a few involved out-of-service trains or overnight maintenance vehicles.

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“Our system is very safe, and we have many men and women who work very hard to maintain and inspect our track, as well as our vehicles and its wheels,” said Jeffrey Gonneville, the MBTA’s chief operating officer. “We are going to be in a far better managed position as it relates to our track inspection oversight than we have ever had at the MBTA.”

MBTA officials attributed the increase in subway derailments to a change in federal standards in 2015, when the Federal Transit Administration began requiring transit agencies to report derailments of vehicles that aren’t meant to carry passengers, including maintenance trucks. Such trucks can be more susceptible to derailments at switch points, Gonneville said.

Last fall, the Globe reported that seven Green Line trains had derailed in 2015, the most light rail derailments in the country that year. An audit found that the MBTA was not adequately maintaining its tracks or the wheels on a type of Green Line car with a history of derailments, and officials had caught drivers speeding.

The jump in derailments on the Green Line over the past two years reversed progress made in recent years. In 2007, 29 Green Line trains jumped the tracks, but by 2012 just one did.

The federal statistics do not include derailments on commuter rail systems, which are reported to the Federal Railroad Administration.

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None of the derailments in 2016 were caused by a collision.

In 2008, a driver was killed when two westbound trains derailed after they collided on the Green Line’s D Branch in Newton.

But other types of derailments can injure passengers. In March 2014, for example, a speeding Green Line trolley smashed into a tunnel wall after jumping the tracks. The crash sent several people to the hospital with minor injuries, including some who were hurt when a second trolley slammed on its brakes to avoid the derailed train.

Derailments can also hobble service for hours. In several of last year's derailments, passengers were transferred to shuttle buses as workers used hydraulic lifts to return trains to the tracks.

In May 2016, a defect with a track switch probably led a Green Line train with 200 passengers to derail near Park Street Station, officials said. Passengers had to get off the train and walk through the tunnel toward Government Center to exit at that station, and it took nearly four hours to resume full Green Line service.

And in October 2016, a derailed Green Line trolley on the B branch led to hours of delays as passengers had to use shuttle buses to connect six stops.

MBTA officials said a Green Line official had not properly thrown a switch at the Boston College stop, and it took almost 2½ hours to get the train back on the rails.

While the audit conducted last year in response to the derailments went unmentioned publicly until a Globe report, MBTA officials have become more open about the problem in recent months.

After the Oct. 30 derailment on the Green Line near the Boston College stop, Gonneville gave a detailed dispatch on the incident at a weekly fiscal and management control board meeting, according to Joe Pesaturo, a T spokesman.

Such problems are much less common on the MBTA’s three subway lines — Red, Blue, and Orange. In 2016, the MBTA recorded its first derailments on the Red and Orange lines since 2001.

But in both cases, the derailments affected vehicles that don’t carry passengers. On May 19, just after 3 a.m., a car for the power department derailed at Davis Station on the Red Line. On July 13, around 3:45 a.m., the rear of another utility vehicle derailed on the Blue Line at Orient Heights as it was headed back to the yard.

The mishaps caused minimal property damage. The May incident broke two third rail insulators, according to an MBTA report. The July incident briefly delayed service because it occurred shortly before train service began for the day.

MBTA officials say they are taking the derailments seriously, but some specialists say they aren’t overly concerning.

“Derailments are a lot more common than people think,” said Robert Paaswell, a civil engineering professor at City College of New York and the former executive director of the Chicago Transit Authority. “You’re talking about hundreds of light rail vehicles for thousands of miles a day.”

Some transit agencies may not report all of their derailments, he added.

On Friday, Gonneville said that the MBTA is planning
initiatives to help prevent derailments. In coming months, workers will be able to see inspection results on a new electronic dashboard to help them pinpoint problem areas on the tracks.

“It’s going to really move us from being more reactive to proactive in our rail maintenance division,” he said.